It's a simple question: "Why not try Jesus?" Equally simple is an opposite: "Why believe in a god?" Yet in the United States the first question is widely viewed as positive, or at least ordinary, while the second can be perceived as offensive and even hate speech.

This difference in reaction can't result from the structure of the statements. They're the same. Nor can it be the tone. Nope, it's just the message. Americans think it's good to believe in a god and bad not to. Furthermore, it's good to tell everyone about your belief but bad to be just as open about nonbelief or doubt – especially during the winter holiday season.

Clearly, American nontheists can't get a break.

We in the American Humanist Association found this out first hand when we launched our Washington DC advertising campaign on November 11 with the slogan "Why believe in a god? Just be good for goodness' sake." The venue was the sides, rears and insides of 230 of the city's buses. News coverage of the campaign generated an outpouring of phone calls and e-mails, mostly negative. The largest number came directly to us but hundreds of complaints also came to Metro, the government entity that handles the city's buses and subways. One of the complainers expressed a wish (or perhaps a prayer): "May all your atheist buses break down!"

The sudden high volume of visitors to our special campaign website www.whybelieveinagod.org crashed our server twice. Soon, the conservative talkshow hosts were clamouring to give us air time so they could argue against us and further rouse their audience. And conservative Christian organisations not only denounced our efforts but encouraged their flocks to come bleat in our ears. All this before our bus ads actually started to appear one week later. By the beginning of December we'd received 37,742 hits on our campaign website, logged 638 new members and received over $6,000 in new contributions.

An ad from the American Humanist Association inside a bus in Washington DC. (Photograph: American Humanist Association)

Now, it seems, we have a couple of competitors. The primary one, a local Catholic stay-at-home mother of four, decided to launch a counter campaign: same types of bus advertisements, same number of buses, same topic. Her slogan? "Why believe? Because I created you and I love you, for goodness' sake." The sentiment is signed, "God". The second competitor, Pennsylvania Friends of Christ, announced an ad on 10 buses that will read, "Believe in God. Christ is Christmas for goodness sake."

This led to more newspaper stories and interviews on radio and television. So much so that the company that handles bus advertising for Metro asked us this week if we would be so kind as to quantify all our results for them so they can inform would-be clients just how effective bus ads can be!

If all this buzz sounds a little familiar, it's because it is. Back in October a story in the Guardian went global about the Atheist Bus Campaign in London. The planned adverts, written by comedy writer and Guardian contributor Ariane Sherine, were designed to read: "There's probably no God. Now stop worrying and enjoy your life." This was in reaction to a widely run Christian campaign threatening unbelievers with hellfire. The British Humanist Association agreed to handle the financial contributions for this effort and was able to raise a whopping £120,402 in the first month. Yet none of the adverts have actually appeared on buses, being slated to hit the streets in January.

Naturally, this excitement affected those of us planning promotional efforts for the American Humanist Association. We'd been trying to work up a splashy advertising campaign for Washington DC buses since July but hadn't figured out an ad slogan we really liked. So, when the news hit about the London plans, it became for us like an inspiration, a revelation – dare I say, a miracle?

We accelerated our work, experimenting with a range of slogans, until finally settling on the one. Then we contracted for the ad space, designed and printed the signs, bought display ads in the New York Times and Washington Post, and the rest followed.

The media is still heated up. There's more to come. But we pause amid the flurry and fury to reach our hands across the pond in gratitude and solidarity with our likeminded friends in the UK. The work of each enhances that of the other as we both let millions of atheists, agnostics and humanists know there are others like them and organisations to serve their needs and advance their ideals.